Rock cakes are a type of small, dense fruitcake traditionally served at teatime. In the Wizarding world, they are most famously and frequently baked by Rubeus Hagrid. Hagrid's particular version of rock cakes lives up to the name literally; they are notoriously and comically hard, often described as being like “fruit-studded cannonballs” and are nearly inedible. They are typically lumpy, greyish, and contain ingredients like currants, though their most defining feature is their texture, which poses a significant risk to the teeth of anyone attempting to eat them. Despite this, Hagrid bakes them with great pride and affection, offering them to his guests as a gesture of warm hospitality.
The primary characteristic of Hagrid's rock cakes is their extreme hardness. On Harry Potter's first visit to Hagrid's Hut, he politely gnawed on one and nearly broke a tooth in the process. This quality makes them a recurring source of gentle humor throughout the series. Consumption is often a matter of diplomacy rather than enjoyment. Harry, Ron Weasley, and Hermione Granger frequently pretend to eat the rock cakes to avoid offending Hagrid. They might crumble them in their pockets or simply leave them on the plate. On at least one occasion, Hagrid's boarhound, Fang, was seen dribbling on a plate of rock cakes, seemingly undeterred by their texture.
Despite being a simple food item, rock cakes serve several important narrative functions.